1. Field of the Disclosure
The present disclosure relates to a light amplifier and a laser processing device, and particularly to a technique of stably generating a light pulse from a fiber amplifier in an MOPA (Master Oscillator and Power Amplifier) system.
2. Background Information
In laser processing devices, the laser beam power influences the processing quality. To address the problem, techniques of controlling the power of laser beam emitted from the laser processing device have been proposed.
For example, Japanese Patent Laid-Open No. 2010-10274 discloses configuration for measuring the average power and the peak power of a laser pulse which is output from a fiber laser oscillator and feeding back the measurements to an LD (laser diode) drive circuit.
Further, Japanese-Patent Laid-Open No. 2010-171131, for example, discloses that the laser light source for emitting seed light to be incident on the fiber laser emits pulsed light during a main radiation period and emits substantially continuous light during a preliminary radiation period. The power of the continuous light is weaker than the peak power of the pulsed light.
Japanese-Patent Laid-Open No. 2010-171131 also discloses that the power of the exciting light of the preliminary radiation period is lowered below the power of the exciting light of the main radiation period.
In the method disclosed in Japanese Patent Laid-Open No. 2010-10274, the average power and the peak power of the laser light pulse are measured.
Since the uniformity of the strength of a plurality of pulses cannot be monitored in the method, it is considered to be difficult to control the strength of a plurality of pulses to be uniform by the method. On the other hand, Japanese Patent Laid-Open No. 2010-171131 does not specifically disclose the configuration for detecting the power of the pulse.
Fiber amplifiers are mostly excited by a laser diode (LD). However, in order to change the laser output of the fiber amplifier, the time period after the output of the exciting LD is changed until the laser output is changed (response time) may be about 1 ms or more. Therefore, as the repetition frequency of the pulses is higher, it becomes more difficult to measure the strength of each pulse and feed the measurements back to the control on the pulse strength. For those reasons, in the fiber amplifiers, the measurements of the average power of the laser output are generally fed back to the control on the laser output.
On the other hand, an LD is mostly used for the light source of the seed light to be input to the fiber amplifier. Therefore, the conditions of the seed light pulse can be varied. For example, the repetition frequency can be changed in a wide range or a group of pulses including a plurality of pulses with the pulse width of about ns can be generated.
When the seed light is changed as described above, the variation range of the peak value is greatly widened. Therefore, in the case of fiber amplifier, it is more difficult to detect the peak value for each pulse. On the other hand, it is required to control the strength of a plurality of pulses to be uniform to stabilize the laser output.
An object of the present disclosure is to provide a technique of detecting a peak value for each output light pulse from a light amplifier which uses a light amplifying fiber.